The invention relates generally to a method for achieving improved transfer case clutch performance and more particularly to a method which determines the clutch current versus torque throughput function and utilizes such determination to achieve improved transfer case clutch performance.
Many four wheel drive vehicles nominally operate in two wheel drive and include sensors and control systems which automatically shift a transfer case clutch to four wheel drive upon detection of a wheel speed difference (Δs) typically between the front and rear wheels. Such adaptive four wheel drive systems are carefully tuned by the vehicle manufacturer, typically through extensive road testing, to achieve desired performance and optimum safety and control. The primary operating parameter so determined is the relationship between wheel slip and the speed and extent of transfer case clutch engagement per unit time (dc/dt) when a threshold quantum of wheel slip is encountered. In such vehicles, the sensing of wheel speed, the computations undertaken to determine wheel slip and the clutch engagement control signal issued when wheel slip is determined are all electronic signals and operations determined and undertaken in accordance with the program or software utilized in the transfer case controller which is either developed or adapted by the vehicle manufacturer.
Such electrical output or drive system to the transfer case clutch assumes an established clutch current versus clutch engagement and torque transfer function. Since the transfer case clutch is an electromechanical or hydromechanical device, the accuracy and repeatability of its operation encompasses wider tolerances than the electronic clutch control system.
The present invention is directed to improving the operation and cooperation and between a motor vehicle transfer case controller and the transfer case clutch.